The present invention pertains to an apparatus for forming a single face web of corrugated paperboard and, more particularly, to a corrugating roll assembly for a single facer.
In the manufacture of corrugated paperboard, a single facer apparatus is used to corrugate the medium web, apply glue to the flute tips on one face thereof, and to bring a liner web into contact with the glued flute tips of the medium web with the application of sufficient heat and pressure to provide an initial bond. A conventional single facer typically includes a pair of fluted corrugating rolls and a pressure roll, which are aligned so the axes of all three rolls are generally coplanar. The medium web is fed between the inter-engaging corrugating rolls and the adhesive is applied to the flute tips by a glue roll while the medium is still on the corrugating roll which comprises the intermediate of the three roll arrangement. The liner web is immediately thereafter brought into contact with the adhesive-coated flute tips in the nip between the pressure roll and the corrugating roll.
As corrugating nip roll pressures and corrugating speeds have increased, changes have been made in the construction of single facers to maintain the quality of the corrugated medium and to attempt to deal with the problems of high noise and vibration. For example, the load between corrugating rolls at the corrugating nip has required that one of the fluted corrugating rolls be made with a crowned surface to accommodate roll deflection under high nip loads. Deflection as a result of high loading is also believed to be one source of noise and vibration. In a conventional single facer construction, where the two corrugating rolls and the lower pressure roll are in general alignment (their axes lying generally coplanar), corrugating roll loads are transmitted to the pressure roll adding further to the problems associated with high loads and high speeds. This has resulted, in some cases, in manufacturing the pressure roll with a negative crown to match deflections in the corrugating roll which together form the nip for joining the two single face web components.
One of the most serious problems in the operation of high speed single facers is the so-called "labyrinth" effect. In order to handle high loads and higher speeds, single facer manufacturers have gone to increasingly larger diameter, heavier and stronger corrugating rolls. As the medium web is drawn into the pressure nip, formed by the inter-engaging flutes on the two corrugating rolls, the medium web begins to be deformed, folded and gathered as it moves into the actual nip centerline where full engagement of the flutes occurs. Larger diameter corrugating rolls inherently create a more tortuous path for the web as the web begins to be wrapped partially around opposite alternating teeth or flutes of the mating corrugating rolls while moving into the fully nipped position. Each wrap of the web encompasses a slightly larger radius around the flute tip as it approaches the nip and each deformation or wrapping of the web on a flute tip adds a tension component to the overall web tension. As indicated, the additive labyrinth effect is increased as the corrugating roll diameters increase and it is not uncommon for the medium web to rupture or tear.
One proposed solution to the labyrinth problem is disclosed in U.S. Pat. No. 3,990,935. The single facer construction disclosed in this patent proposes to maintain relatively small diameter corrugating rolls to minimize the labyrinth length and to provide internally pressurized flexure compensation for the inevitable bowing to which the rolls are subjected under high corrugating nip loads. Another proposed solution to the labyrinth effect is described in U.S. Pat. No. 4,531,996. In accordance with this patent, the upper corrugating roll contact with the lower corrugating roll is "dephased" by dividing the upper roll into axially adjacent segments each of which makes nip contact with the other corrugating roll at a different point. Alternately, the dephasing effect is provided by making the segments of the upper corrugating roll of different diameters. Both of the foregoing solutions require extremely complex roll constructions.